Conventional sensor systems have been developed from various materials that change color upon exposure to a target molecule. Such sensor systems are generally based on photonic crystals that have been modified to recognize the target molecule. The photonic crystal contains periodic nanostructures with differing indices of refraction that interact with visible light. The material recognizes or binds to specific chemical targets. Recognition of the target alters the spacing of the periodic nanostructure, thereby changing the way it interacts with visible light.
The advantage of such systems lies in producing a discernable change in color. This concept has been applied in the fabrication of colloidal hydrogel systems, porous silicon systems, as well as through the use of lithography techniques on other substrates. The use of a photonic crystal polymerized colloidal hydrogel system has been demonstrated (Cui et al. (2009) Analyst 134(5):875-880; Lee, K., Asher, S. A. (2000) Journal of the American Chemical Society 122(39):9534-9537. Such material could act as a sensor for glucose but required the complex process of synthesizing monodisperse, highly charged polystyrene particles. Porous silicon (Lee, M., Fauchet, P. M. (2007) Optics Express 15 (8), 4530-4535; Li et al. (2003) Science 299(5615): 2045-2047) and nanoprint lithography (Endo et al. (2010) Sensors and Actuators B: Chemical 148(1):269-276) have also been reported as photonic crystal chemical sensing platforms. The observed response in such conventional systems, however, is small, non-visible, and thus cannot be measured without the aid of supplementary equipment and further analytical measurements.
Therefore, there is a need for a sensor that can be easily fabricated, and yield an instantaneous, visibly discernable response.